The present invention relates to a process for treating solutions of a hydroxylammonium salt containing excess acid. More particularly, the present invention relates to the production of highly pure aqueous solutions of hydroxylammonium nitrate of high concentrations.
Hydroxylammonium nitrate has several commercial applications, such as in the purification of plutonium metal, as one component of a liquid propellant, and as a reducing agent in photographic applications. In some of these applications a highly purified form of the compound is required, especially when it is to be employed in propellant formulations where the hydroxylammonium nitrate (HAN) solution is stable in an aqueous solution, but must be substantially free of excess acids as well as transition metal elements, such as iron and copper.
High purity hydroxylammonium salt solution such as hydroxylammonium nitrate can be produced in an electrochemical process described in U.S. Pat. No. 4,849,073 issued Jul. 18, 1989 to R. L. Dotson et al. The process feeds nitric acid to the cathode compartment of an electrochemical cell having a separator between the anode and cathode compartment. The catholyte is electrolyzed at a temperature below about 50.degree. C. and a cathode half-cell potential at from about -0.5 to about -3 volts to produce a hydroxylammonium nitrate solution. This solution is acidic, containing an excess of nitric acid.
Neutralization of the excess acid is described in U.S. Pat. No. 4,968,394, issued Nov. 6, 1990 to R. L. Dotson et al. The excess acid can be neutralized by mixing hydroxylamine vapor or nitric oxide with the hydroxylammonium nitrate containing excess acid. The excess acid in the solution is converted to hydroxylammonium nitrate. U.S. Pat. No. 4,968,394 further teaches that the excess acid can be reduced by contacting hydroxylammonium nitrate containing excess acid with a basic anion exchange resin. Preferably the anion exchange resin has a pKa in the range of 5 to 9.
However, direct contact of a basic anion exchange resin with a hydroxylammonium nitrate solution containing excess nitric acid results in oxidation of the resin by the nitric acid with accompanying decomposition and loss of capacity.